Question

Name a gas which turns:
Starch iodide paper blue black

Answer 1

1. The gas is Chlorine, $C{l}_2$.
2. Chlorine gas turns starch iodide paper blue-black. Iodine ($I_2$) gets reduced to Iodide ions ($I_3^{-}$).

$I_2\left(s\right)+I^{-}\left(aq\right)\to {I_3}^{-}\left(aq\right)$

Iodine Iodide Ion Iodide Ion

Chlorine gas,$C{l}_2$ , turns starch iodide paper blue-black.